The present invention generally relates to the field of electronic scan phased-array radar antennas, such as might be used in airborne ground-mapping systems and is specifically concerned with a manifold structure capable of accommodating a high density of phase control modules in such antennas.
A typical electronic scan radar antenna is constructed on an elliptical aluminum plate about two feet by four feet in dimension. Several hundred holes are drilled in the plate at predetermined intervals, and several hundred phase control modules (PCMs) are mounted so that one PCM protrudes from each hole. The PCM devices can be controlled to transmit and receive RF signals in a desired pattern so that the antenna can scan a selected geographical area without the need for moving parts.
FIG. 1 illustrates the prior art structure by which the PCMs 105 are coupled to the system's RF transmitting and receiving equipment using RF waveguides known as manifolds. In the prior art, such antennas have used a waveguide branch manifold structure in which RF signals are carried through a plurality of rectangular main manifold feeds (not shown) which are connected to branch manifolds 101 by a coupling flange. The signals are transmitted through the branch manifold 101 and through cross waveguides 104 to the PCMs 105. The cross waveguides 104 are attached to the branch manifolds 101 and spaced according to the desired PCM spacing, which will determine the characteristics of the antenna. The branch manifolds 101 are usually deployed in parallel, horizontally across the antenna, to connect the PCMs 105 and are also connected (according to the quadrant of the antenna they are located in) to one of four main manifold feeds (not shown in FIG. 1) which are connected to the transmitter and receiver. The manifold feeds are deployed vertically. A load is provided to absorb excess signals at the end of each branch manifold 101 and cross waveguide 104.
This prior art design functions well in antennas where closely spaced PCMs 105 are not required. However, as the technology of phased array antennas progresses, so that smaller antennas with better RF performance and higher power handling capability are desired and developed, tight spacing of PCMs 105 is becoming an important requirement. Rectangular waveguides which are able to carry the desired signal frequencies and power levels may have a cross-sectional width "A" larger than the desired PCM spacing "B". Constructing an antenna with horizontal main manifolds and a PCM spacing "B" of less than the required width "A" of the cross waveguides 104 is physically impossible, because a plurality of cross waveguides 104 would have to share the same physical space.
It is known to orient the branch manifolds diagonally rather than horizontally, but this method has not been completely satisfactory. With diagonal branch manifolds, the attachment of the quadrant manifolds to the branch in the manifold assemblies becomes quite complex. This technique, known as quadranting the antenna array, is desirable to improve signal processing capabilities.
An additional problem arises as the power to be transmitted by phased array radars increases. At high power levels, the manifold waveguide structure will become quite hot. Therefore, for high power systems, cooling may be desired. However, many tightly constructed prior art systems have no provision for either air or liquid cooling of the manifold waveguide structure.
Therefore, there is a need for an improved antenna manifold assembly that allows close PCM spacing while maintaining a horizontal and vertical (nondiagonal) manifold structure which permits quadranting of the antenna array. In addition, there is a need for antenna manifold assemblies that are adapted for fluid cooling so that high power levels can be used.